Combined sensor for the transcutaneous measurement of oxygen and carbon dioxide in the blood

Abstract

The combined sensor with a thermostatted heating device (7, 23) for the simultaneous and continuous transcutaneous measurement of oxygen (O 2 ) and of carbon dioxide (CO 2 ) in the blood contains a measuring device (1) for the partial pressure of CO 2 (pCO 2 ), in which there is pure optical/spectrometric operation or which operates on the principle of pH measurement in a electrolyte (8), and which is separated from the measuring site on the skin by a membrane (13) which is permeable to both CO 2 and light, and contains another measuring device (24, 25, 26) for the spectrometric measurement of the blood oxygen saturation (sO 2 ). The advantage over a known pO 2 /pCO 2 combined sensor is that the combined sensor according to the invention can be operated at a low operating temperature of, for example, 42° C. or less, so that continuous measurement for 24 hours, for example, is possible without resiting or recalibrating the sensor, and thus it is simple to use in the domestic milieu.

I claim: 
     
       1. A sensor element for simultaneous, continuous, transcutaneous measurement of the partial pressure of carbon dioxide and the oxygen saturation in the blood of a living body, said sensor element comprising: a housing having a planar measuring surface;   a membrane permeable to carbon dioxide, sealably disposed about the measuring surface, said membrane having inner and outer surfaces;   two light emitting diodes embedded in the measuring surface each emitting light of different wave lengths and positioned so that the emitted light beams do not mutually interfere;   photoelectric receiving means embedded in the measuring surface;   a thin layer of electrolyte disposed between the measuring surface and the inner surface of the membrane;   a third light emitting diode and an adjacent photoelectric receiving unit in the measuring surface;   an intermediate layer of color indicator in the measuring surface which covers said third light emitting diode and said adjacent photoelectric receiving unit;   whereby when the outer surface of the membrane is brought into contact with the skin, carbon dioxide diffuses through the membrane changing the pH of the electrolyte solution, which changes in pH alters the light absorption or light reflection properties of said layer of color indicator and is detected by diffusing the light emitted from the third light emitting diode through the skin and detecting it by the adjacent photoelectric receiving unit under the color indicator layer and whereby the light emitted from the two light emitting diodes after diffusion through the skin is detected by the photoelectric receiving means and the oxygen saturation of the blood is determined by the principle of pulse oximetry.   
     
     
       2. The sensor of claim 1 wherein the color indicator is a thin layer of acrylic resin embedded as an intermediate layer in the measuring surface. 
     
     
       3. The sensor of claim 2 wherein the two light emitting diodes and the photoelectric receiving means are inserted in depressions in the measuring surface which are filled with resin. 
     
     
       4. The sensor of claim 1 wherein the two light emitting diodes and the photoelectric receiving means are inserted in depressions in the measuring surface which are filled with resin.